What must be present in the WPFR device for it to function properly?

The correct answer indicates that a cleat must be present in the WPFR (Work Positioning Fall Restraint) device for it to function properly. A cleat serves as a critical component that provides a secure attachment point, allowing the user to safely position themselves while working at heights. In the context of fall protection, the cleat offers stability and prevents unintended movements that could lead to falls. Ensuring that the cleat is in place is essential for the overall safety and effectiveness of the WPFR device.

While the other components mentioned may play roles in different safety equipment or scenarios, they do not specifically pertain to the functionality of the WPFR device. For instance, a warning light could alert individuals to hazards but does not assist in fall restraint, a safety net provides passive fall protection but is not part of a WPFR system, and a harness is crucial for many fall protection systems but needs the cleat as part of the WPFR setup to ensure safety when positioning at height.